Eleven large PR firms have pledged to clean up the way they interact with Wikipedia, the online encyclopaedia.

Before now many surreptitiously edited pages about their clients via pseudonymous accounts.

Eleven firms have now signed a pledge to follow the online encyclopaedia's rules when they want entries changed.

Dialogue with PR firms started after Wikipedia's overseers threatened one firm with legal action over the way it edited pages.

In late 2013, the Wikimedia Foundation, which runs Wikipedia, said it was investigating more than 300 accounts it believed were fakes set up by people acting for just one PR agency seeking to remove damaging information from entries.